1. Field of the Invention
The invention relates to a heatable gas analysis device.
2. Description of the Related Art
In gas analysis, heatable analysis devices are used when the gas to be analyzed (i.e., the measurement gas) contains moisture, and when condensation in the device is meant to be prevented. To this end, for example, the entire device may be heated by circulated-air, so that the gas paths in the device are brought to a predetermined uniform operating temperature. In this case, at the interfaces with the environment of the device, i.e., in the regions of the measurement gas input and output, additional heaters may be provided for the gas paths. There are also gas analyzers comprising gas sensors, in particular based on semiconductor metal oxides, which need to be heated in order to be able to perform meaningful measurements. In gas chromatographs, heating of the separating column is often necessary to achieve the desired separation properties, or the sample to be analyzed is a liquid that needs to be evaporated before it enters the separating column. Since conventional gas analysis methods are generally temperature-sensitive, not least the influence of external temperature can be reduced by heating the analysis device, and the measurement result can thereby be stabilized.
DE 196 01 571 A1 discloses a gas chromatograph comprising two separately thermally regulatable separating columns, of which one separating column is arranged in an oven and the other separating column is coiled outside the oven on an electrically heatable heating body.
In a method known from DE 43 08 936 A1, in order to calibrate a measurement device, such as a gas analysis device, in which the sensitivity and zero point can vary during operation because of heating of the physical part after switching on and because of temperature gradients, a plurality of calibration values are measured at time intervals. With a predetermined number of most recently measured calibration values, via a nonlinear function, future calibration values, with which the measurement values are corrected, are calculated.
From DE 695 33 019 T2, it is known to control the temperature in a predetermined zone of an analytical instrument by subjecting a heating fluid to an exothermic chemical reaction in a convertor and delivering the heat generated thereby into the zone. The flow of heating fluid into the convertor is regulated as a function of the temperature measured in the zone. It is additionally possible to use a cooling fluid for cooling, which is subjected to an endothermic chemical reaction.
Here and in what follows, heating of the gas analysis device is not necessarily intended to mean heating of the entire device. In most cases, the heating is restricted to the analysis part or module, with the measurement components contained therein directly recording the measurement gas, through which the measurement gas flows. In the case of a non-dispersive infrared (NDIR) gas analyzer, these are for example an infrared radiator, a measurement-gas cell and optionally reference-gas cell, and an opto-pneumatic detector arrangement.
After the analysis device is switched on, it is a general practice to wait until the device, or the analysis part, has reached operating temperature, the temperature having to lie within a specified tolerance so that the analysis part is capable of measurement.
Correct construction and the stability of the mechanical components of the analysis part are indispensable for correct measurement value acquisition. If, during manufacture of the device, the construction does not correspond to the specification, or the mechanical stability weakens during subsequent operation, this can have a serious effect on the measurement value acquisition. Testing is therefore generally performed by visual inspection with the device open. Unacceptable deviations can be identified by calibration with a test gas, and leaks can be identified by a pressure test.